This is an experimental technologyBecause this technology's specification has not stabilized, check the compatibility table for usage in various browsers. Also note that the syntax and behavior of an experimental technology is subject to change in future versions of browsers as the specification changes.

The operands in the expression may be any length syntax value. You can use different units for each value in your expression, if you wish. You may also use parentheses to establish computation order when needed.

Note: Division by zero results in an error being generated by the HTML parser.

Note: The + and - operators must always be surrounded by whitespace. The operand of calc(50% -8px) for instance will be parsed as a percentage followed by a negative length, an invalid expression, while the operand of calc(50% - 8px) is a percentage followed by a minus sign and a length. Even further, calc(8px + -50%) is treated as a length followed by a plus sign and a negative percentage.
The * and / operators do not require whitespace, but adding it for consistency is allowed, and recommended.

Note: Math expressions involving percentages for widths and heights on table columns, table column groups, table rows, table row groups, and table cells in both auto and fixed layout tables MAY be treated as if auto had been specified.

Examples

Positioning an object on screen with a margin

calc() makes it easy to position an object with a set margin. In this example, the CSS creates a banner that stretches across the window, with a 40-pixel gap between both sides of the banner and the edges of the window:

Here, the form itself is established to use 1/6 of the available window width. Then, to ensure that input fields retain an appropriate size, we use calc() again to establish that they should be the width of their container minus 1em. Then, the following HTML makes use of this CSS:

Nested calc() with CSS Variables

After all variables are expanded, widthC's value will be calc( calc( 100px / 2) / 2), then when it's assigned to .foo's width property, all inner calc()s (no matter how deeply nested) will be flattened to just parentheses, so the width property's value will be eventually calc( ( 100px / 2) / 2), i.e. 25px. In short: a calc() inside of a calc() is identical to just parentheses.